Optical systems are widespread and often include a light source or sources and a system of optical elements. A typical image display system incorporates an illumination source that is arranged so that light rays from the illumination source reflect off of an image-forming device or imager that contains the desired image to be projected. One common type of imager is a polarization-rotating image-forming device, such as a liquid crystal on silicon (LCoS) device, which operates by rotating polarization of the incident light rays. More particularly, in a reflective polarization-rotating imager, polarized light rays are either reflected with their polarizations substantially unmodified for the darkest state or reflected with their polarizations rotated to provide a desired gray scale.
In some image display systems, a light beam originating from a light source or an assembly of light sources may be split into two or more beams traveling in different directions, which may or may not be recombined further downstream. In other types of optical systems, light beams originating from different light sources or light source assemblies may initially travel in different directions, and also may or may not be recombined further downstream. Such multi-directional optical systems are usually relatively complex and include large numbers of various optical elements. Folding mirrors are commonly used to fold the optical paths and thus reduce the footprints of large complicated optical systems.